update the doc for Lwt_unix.{recv,send}_msg
update the doc for Lwt_unix.{recv,send}_msg

Ignore-this: 3a9f33045b388e74ad8a14661301e767

darcs-hash:20130408205322-c41ad-01b5579b5b1c30442c7b03b271c99b471de1b6c1.gz

avsm/lwt-OLD,avsm/lwt-OLD